x86/vmware: use BIT() macro for shifting

[PATCH v4] x86/vmware: use BIT() macro for shifting

Posted by Shreenidhi Shedi 3 years, 11 months ago

From: Shreenidhi Shedi <sshedi@vmware.com>

Using BIT() macro improves readability & it uses unsigned long for
shifting which is an added advantage.

Kernel builds with -fno-strict-overflow CFLAG hence shifting a signed
integer by 31 bits is not an issue in this case.

Signed-off-by: Shreenidhi Shedi <sshedi@vmware.com>
---
 arch/x86/kernel/cpu/vmware.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index c04b933f4..02039ec35 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -476,8 +476,8 @@ static bool __init vmware_legacy_x2apic_available(void)
 {
 	uint32_t eax, ebx, ecx, edx;
 	VMWARE_CMD(GETVCPU_INFO, eax, ebx, ecx, edx);
-	return (eax & (1 << VMWARE_CMD_VCPU_RESERVED)) == 0 &&
-	       (eax & (1 << VMWARE_CMD_LEGACY_X2APIC)) != 0;
+	return !(eax & BIT(VMWARE_CMD_VCPU_RESERVED)) &&
+		(eax & BIT(VMWARE_CMD_LEGACY_X2APIC));
 }

 #ifdef CONFIG_AMD_MEM_ENCRYPT
--
2.36.1

Re: [PATCH v4] x86/vmware: use BIT() macro for shifting

Posted by Srivatsa S. Bhat 3 years, 10 months ago

On 6/1/22 3:18 AM, Shreenidhi Shedi wrote:
> From: Shreenidhi Shedi <sshedi@vmware.com>
> 
> Using BIT() macro improves readability & it uses unsigned long for
> shifting which is an added advantage.
> 
> Kernel builds with -fno-strict-overflow CFLAG hence shifting a signed
> integer by 31 bits is not an issue in this case.
> 
> Signed-off-by: Shreenidhi Shedi <sshedi@vmware.com>
> ---

Looks good to me.

Reviewed-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>

>  arch/x86/kernel/cpu/vmware.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
> index c04b933f4..02039ec35 100644
> --- a/arch/x86/kernel/cpu/vmware.c
> +++ b/arch/x86/kernel/cpu/vmware.c
> @@ -476,8 +476,8 @@ static bool __init vmware_legacy_x2apic_available(void)
>  {
>  	uint32_t eax, ebx, ecx, edx;
>  	VMWARE_CMD(GETVCPU_INFO, eax, ebx, ecx, edx);
> -	return (eax & (1 << VMWARE_CMD_VCPU_RESERVED)) == 0 &&
> -	       (eax & (1 << VMWARE_CMD_LEGACY_X2APIC)) != 0;
> +	return !(eax & BIT(VMWARE_CMD_VCPU_RESERVED)) &&
> +		(eax & BIT(VMWARE_CMD_LEGACY_X2APIC));
>  }
> 
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
> --
> 2.36.1
>  
Regards,
Srivatsa
VMware Photon OS

[tip: x86/vmware] x86/vmware: Use BIT() macro for shifting

Posted by tip-bot2 for Shreenidhi Shedi 3 years, 10 months ago

The following commit has been merged into the x86/vmware branch of tip:

Commit-ID:     4745ca43104b422354f06dc814d3f13661f217af
Gitweb:        https://git.kernel.org/tip/4745ca43104b422354f06dc814d3f13661f217af
Author:        Shreenidhi Shedi <sshedi@vmware.com>
AuthorDate:    Wed, 01 Jun 2022 15:48:20 +05:30
Committer:     Borislav Petkov <bp@suse.de>
CommitterDate: Wed, 22 Jun 2022 11:23:14 +02:00

x86/vmware: Use BIT() macro for shifting

VMWARE_CMD_VCPU_RESERVED is bit 31 and that would mean undefined
behavior when shifting an int but the kernel is built with
-fno-strict-overflow which will wrap around using two's complement.

Use the BIT() macro to improve readability and avoid any potential
overflow confusion because it uses an unsigned long.

  [ bp: Clarify commit message. ]

Signed-off-by: Shreenidhi Shedi <sshedi@vmware.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Link: https://lore.kernel.org/r/20220601101820.535031-1-sshedi@vmware.com
---
 arch/x86/kernel/cpu/vmware.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index c04b933..02039ec 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -476,8 +476,8 @@ static bool __init vmware_legacy_x2apic_available(void)
 {
 	uint32_t eax, ebx, ecx, edx;
 	VMWARE_CMD(GETVCPU_INFO, eax, ebx, ecx, edx);
-	return (eax & (1 << VMWARE_CMD_VCPU_RESERVED)) == 0 &&
-	       (eax & (1 << VMWARE_CMD_LEGACY_X2APIC)) != 0;
+	return !(eax & BIT(VMWARE_CMD_VCPU_RESERVED)) &&
+		(eax & BIT(VMWARE_CMD_LEGACY_X2APIC));
 }
 
 #ifdef CONFIG_AMD_MEM_ENCRYPT